Polyethylene base resin composition having highly filled with an inorganic material

ABSTRACT

The composition of this invention is a polyethylene base resin composition containing a high concentration of an inorganic material, which has high flame retardancy and sufficient tensile elongation for practical application and is adapted to be used as a raw material for a field in which high flame retardancy is demanded such as coatings for flame retardant wires and cables and flame retardant raw material of foamed product. This composition mainly consists of a resin component formed of 10 to 75 parts by weight of polyethylene having a density ranging between 0.910 and 0.945 (g/cm 3 ) and a melt index ranging from 0.01 to 2.0 (g/10 min) and 90 to 25 parts by weight of an ethylene-base copolymer and further contains 80 to 250 parts by weight of powder of a hydrated metal oxide on the basis of 100 parts by weight of the resin component of said polyethylene base resin composition.

TECHNICAL FIELD

This invention relates to a novel polyethylene base resin compositionwhich is prepared by filling a blend polymer consisting of polyethyleneand an ethylene-base copolymer with a high concentration of hydratedmetal oxide; is rendered extremely flame-retardant; preserves sufficientextensibility for practical application; when purposely subjected tocombustion, produces a considerable amount of self-cohesive ash; and hashigh foam properties.

BACKGROUND ART

With polyolefins, such as polyethylene, polypropylene, polybutane-1,ethylene-propylene rubber, the oxygen index specified in the JapaneseIndustrial Standards JIS K 7201-1976 entitled "Combustion test method ofpolymers by the oxygen index method" ranges between 17 and 19. Among theplastics, the above-listed polyolefins are most inflammable and regardedas difficult to be rendered highly flame-retardant. Particularlypolyethylene, a general-purpose resin, has excellent properties exceptcombustion characteristic and is most inexpensive synthetic polymer.Therefore, a strong demand is made to render this polymerflame-retardant. Accordingly, development is strongly pushed for aprocess of ensuring the uninflammability of polyethylene. Theconventional process of rendering polyolefins flame-retardant comprises:(1) addition of halogen compounds, (2) addition of halogencompounds+antimony trioxide, (3) addition of halogencompounds+phosphorus compounds. It is considered indispensable to applyhalogens such as chlorine or bromine in order to render polyolefinsflame-retardant. However, addition of a halogen series flame-retardantis indeed prominently useful to ensure the flame-retardancy ofpolyolefins, but is accompanied with the drawbacks that when combusted,the polyolefins noticeably evolve black smokes and corrosive and noxiousgases including carbon monoxide and gases released from halogen-bearingcompounds. In recent years, therefore, it is very much desired todevelop a process of ensuring the flame retardancy of polyolefins.Therefore, various processes have been proposed which comprise additionof a special smoke retardant such as molybdenum trioxide to polyolefinsor mixing of polyolefins with an inorganic material. To date, however,no practically acceptable process has been established. Among theseproposed processes, mixing of polyolefins with an inorganic materialattracts attention as a most useful means from the standpoint of savingnatural resorces, facilitating incineration and eliminatingenvironmental polutions as recently demanded from other circles ofsociety.

For example, Japanese Patent Publication No. 51-34866 sets forth aflame-retardant composition containing ethylene-vinyl acetate copolymer,silane and hydrated inorganic filler. This composition is intended forinsulation of building wiring, implement wiring and automobile wiringand undergoes cross-linking at a very high rate of 95% by irradiation ofhigh energy electron application of a chemical cross-linking agent. Theabove-mentioned Japanese Patent Publication No. 51-34866 simplydescribes that a small amount of any other cross-linking polymer, thoughharmful, may be added to the aforesaid ethylene-vinyl acetate copolymerrequiring addition of a silane compound, but such a polymer blend is notpreferred for said invention.

Japanese Patent Disclosure (Kokai) No. 49-78741 discloses that it ispossible to obtain an olefinic resin composition having excellentheat-collecting and heat-insulating properties by adding aluminatrihydrate and metal oxide to a blend polymer consisting ofethylene-vinyl acetate copolymer and polyolefin resin. This invention isnot characterized by applying a special type of polyethylene, but ischaracterized in that it is indispensable to add a metal oxide to ensurethe effect of a heat-collecting property. With this invention, a fillerof alumina trihydrate and metal oxide are applied in as large a totalamount as over 1,000 phr (parts per hundred) of resin. Theethylene-vinyl acetate copolymer is added to elevate the adhesivity ofthe product to, for example, an aluminium board.

Japanese Patent Disclosure (Kokai) No. 50-145448 and Japanese PatentDisclosure (Kokai) No. 52-12134 respectively refer to a filler andcomposition containing a titanate series compound. These inventionsdescribe that one of the favorable effects resulting from addition of atitanate series compound is to increase the elongation at break ofvarious polymers. However, the properties set forth in said inventionsare still unsatisfactory for the object of the present invention. Inother words, the disclosed inventions simply refer to the effect of thehigh extensibility of the product.

DISCLOSURE OF INVENTION

Unlike the above-mentioned techniques, the present invention hasdeveloped a flame-retardant polyethylene resin composition having quiteepoch-making characteristics which, though rendered flame-retardant byaddition of a large amount of an inorganic material, still preservessubstantially the same thermally softening property as polyethylene andmoreover high extensibility; when burned, produces a large amount ofself-cohesive ashes as a combustion residue; and further has high foamproperties. The flame-retardant polyethylene base resin composition ofthis invention is characterized in that said composition mainly consistsof 10 to 75 parts by weight of polyethylene having a density of 0.910 to0.940 (g/cm³) and a melt index of 0.01 to 2.0 (g/10 min) and 90 to 25parts by weight of ethylene-base copolymer, and 80 to 300 parts byweight of powder of hydrated metal oxide are added on the basis of 100parts by weight of the resin component of said polyethylene base resincomposition.

To render polyolefins highly flame-retardant by adding highconcentration of an inorganic material, the present inventors observedthe combustion behavior of a composition consisting of variouspolyolefins such as polyethylene, polypropylene, polybutane-1,ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, andethylene-propylene rubber, blends of said polyolefins with othercompounds, inorganic fine powders added to the base polymer such as finepowders of inorganic materials of, for example, calcium carbonate, clay,aluminium hydroxide and magnesium hydroxide, silane coupling agent knownto elevate the dispersibility and reinforcing effect of said finepowders of inorganic materials, surface beating agent such as a titanateseries compound and various lubricants for increasing the workability ofthe subject composition. The present inventors further evaluated theflame retardancy of the subject composition with reference to an oxygenindex, and the mechanical properties of said subject composition by atensile strength test. As a result, the present inventors havediscovered that a composition prepared by adding a hydrated metal oxideto a polymer blend prepared from specified proportions of a particulartype of polyethylene and a particular type of ethylene-base copolymerpreserves a synergetically high flame retardancy and extensibility and,when burned, characteristically produces a large amount of self-cohesiveashes and also has high foam properties.

The product of this invention has the following characteristics:

(1) The product is a highly flame-retardant polyethylene-base resincomposition which contains powders of an inorganic material andindicates an oxygen index of over 24 and an oxygen index the same as orhigher than that of soft vinyl chloride resin.

(2) Though containing a large amount of powder of an inorganic material,the product indicates an elongation at break of over 350% as determinedby a tensile strength test specified in the Japanese IndustrialStandards JIS C3005-1977 on "The method testing electric wires insulatedby plastics". The product has sufficiently satisfactory properties as,for example, cable sheath material and foam material. In other words,the product retains the original great toughness or high extensibilityand great mechanical strength of the base polymer.

(3) Though comprising an inflammable plastics compound as a basematerial, the product produces a large amount of self-cohesive ashesafter burned, and can be expected to carry out electric and thermalinsulation and surface protection.

(4) Polyolefins containing a large amount of powder of an inorganicmaterial generally has the drawback that foaming gas noticeably escapesat the time of foaming. However, the product is not likely to give riseto such event, but in readily foamable. Moreover, the resultant foamedmass still retains the above-mentioned properties.

(5) The product has excellent workability such as readiness for kneadingand extrusion.

The reason why the composition of this invention displays theabove-mentioned characteristics is not yet clearly defined. However, itis assumed that the extremely fine structure of a polymer matrix and thestructure of an interface between a polymer and an inorganic materialbring about a desirable condition. A multi-component product like thecomposition of the invention which is formed of more than two types ofpolymers and a powder of inorganic material has an extremely intricateand fine structures as viewed from the state in which moleculesimmediately related to the quality of said multi-component product areagglomerated. A matrix phase itself consisting of polyethylene andethylene base copolymer also has a complicated structure. Though themolecules of both polymers indicate a compatible portion, yet thecrystallized section of polyethylene is supposed to be free from themolecules of an ethylene base copolymer. An interface region between thepowder of an inorganic material and the polymer matrix having theaforesaid extremely fine structure has too complicated a moleculearrangement for us to clearly define. Yet, the structure of saidinterface region probably constitutes an important source from which thecharacteristic quality of the composition of the invention originates.For example, the high extensibility of said composition results from thefact that the phase of the polymer matrix can be very much elongated. Inthis case, the structure of the aforesaid interface region should not bechanged to such extent that the polymer matrix is disrupted. Further, alayer comprising air bubbles produced when a foam material is melted athigh temperature should be extended biaxially without rupture. Moreover,the excape of foam gas from the interface between the polymer andinorganic material should be suppressed. The burning of the subjectcomposition involves various factors such as heat transmission in thepolymer section, thermal decomposition thereof, resultant evolution ofinflammable gases and spread of flames. However, the structure of theinterface between the polymer section and uninflammable inorganicmaterial will evidently have a prominent effect on the burning conditionof the subject composition. Therefore, difference in the type of thesubject composition probably leads to unexpectedly noticeable variationsin the degree of the flame retardancy of said composition and thephysical condition of combustion residue.

As described above, polyethylene, ethylene-base copolymer and hydratedmetal oxide seem to have taken a synergetic action in controlling thestructure of an interface region between the polymer and inorganicmaterial which is closely related to the property of the subjectcomposition.

The most decisive factor of said synergetic action is assumed thatpolyethylene having a prescribed density and melt index has beenselected.

The density of polyethylene is an index reflecting the molecularstructure thereof. Polyethylene which acts as one of the base polymersof the subject composition and whose density ranges between 0.910 and0.945 g/cm³ is assumed to be the type having a density ranging betweenthe low and medium levels, and containing a relatively large number ofbranches in the molecular chain. This assumption is supported by thevalue (determined by the infrared absorption spectrum analysis) of thelight absorption coefficient K'770 at the time of peak absorption ofwaves 770 cm⁻¹ resulting from the ethyl branch and the branch of anyother radical having a longer chain than the ethyl radical.

The above-mentioned branching of polyethylene has presumably elevatedthe compatibility of said polyethylene with an ethylene-base copolymerused as one of the base polymer, thereby exerting a favorable effect onthe structure of an interface region between the polymer and inorganicmaterial. Therefore, the subject composition is characterized in that,even where a large amount of powder of inorganic material is added, thesubject composition still retains high extensibility and is renderedsufficiently flame-retardant for foaming, and, when burned, produces alarge amount of self-cohesive combustion residue.

Best Mode of Carrying Out the Invention

Polyethylene which constitutes the most important factor of theabove-mentioned composition of this invention should indispensably bethe particular type whose density ranges between 0.910 and 0.945 g/cm³,and whose melt index (MI) ranges from 0.01 to 2.0 g/10 min.

As used herein, the term "polyethylene" is defined to be the genericname of all polymers. As classified by the method of manufacture(polymerization), the polyethylene includes the high pressure type,medium and low pressure type and radiation polymerized type. Further,the medium and low pressure polyethylene is classified into the Philipsprocess type, standard process type and Ziegler process type withrespect to a polymerization catalyst. Also classification based on thedensity of polyethylene is widely accepted. There are known the lowdensity polyethylene, medium density polyethylene and high densitypolyethylene. As described above, a large variety of polyethylene isprovided. The density of polymer is generally known to reflect itsstructure. However, this structure largely depends on the structure andquantity of branch chains included in the molecular chains. Further,branching can be controlled by adding a small amount of α-olefins suchas propylene and butene-1 as a component of a copolymer.

Therefore, the term "polyethylene", as used herein, includes not onlypolyethylene polymerized from ethylene alone, but also the typepolymerized from ethylene and α-olefins other than ethylene.

Among the above-mentioned various types of polyethylene, the objectpolyethylene used in this invention is limited to the type whose densityand melt index are specified.

Particularly where that type of polyethylene is used in which the valueof the light absorption coefficient K'770 cm⁻¹ is determined to rangebetween 0.5 and 6 by the following equation defining the presence of thebranch of any other radical having a lower chain than the branch of theethyl radical, then the composition of this invention is most preferredbecause it prominently displays its effect. ##EQU1##

where: d=polymer density, l=film thickness (cm), I_(o), I=percentagepermeability (%) at the base line and also of a sample as determined bythe base line method.

As used herein the term "ethylene-base copolymer" includesethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer,ethylene-α-olefin copolymer in which the light absorption coefficienthas a value ranging between 7 and 15, and ethylene and propylenecopolymer.

The above-listed ethylene-base copolymers mainly consist of ethylene(which accounts for more than 50 percent by weight) and anothercomonomer as a secondary component. Where the content of a comonomer isexceedingly small (less than 5 percent by weight), then the mass doesnot exhibit any characteristic quality. In this specification,therefore, such mass is not referred to as an ethylene-base copolymer.

If containing 5 to 75 percent by weight of vinyl acetate as a comonomer,then an ethylene-vinyl acetate copolymer used in this invention wellserves the purpose either as a random type or as a block type. Further,it is possible to apply said random or block copolymer in a partlysaponified form. If the content of the vinyl acetate falls below thelower limit, then the resultant copolymer does not display aflame-retarding behavior characterizing the composition of thisinvention. If the content of the vinyl acetate increases over the upperlimit, then said vinyl acetate presents difficulties in being renderedcompatible with polyolefins.

To provide a drip-free composition specified in UL-94 verticalcombustion test method, it is preferred to apply an ethylene-vinylacetate copolymer containing more than 50 percent by weight of vinylacetate. Further, this ethylene-vinyl acetate copolymer is desired tohave a melt index smaller than 20, or preferably 10.

An ethylene-ethyl acrylate copolymer used in this invention containsmore than 5 percent by weight of ethyl acrylate. Where the content ofthe ethyl acrylate falls below this range, then an ethylene molecularchain present in the copolymer excessively promotes the crystallinity ofthe copolymer, failing to display the effect of the subject composition.

An ethylene-propylene copolymer used in this invention contains morethan 50 percent by weight of ethylene, and includes the so-calledethylene-propylene rubber and terpolymer consisting ofethylene-propylene-diene. The content of propylene is preferred to be 10to 50 percent by weight.

It has been discovered during the process of preparing the compositionof this invention that only that type of the ethylene-propylene-dieneterpolymer which contains dicyclopentadiene as a third component iseffective for the prevention of the occurrence of drips specified in theUL-94 vertical combustion test. Where, therfore, it is intended toensure the flame retandancy of the subject composition, particularly theprevention of occurrence of drips during the vertical combustion, it ispreferred to apply the ethylene-propylene-diene terpolymer.

The reason runs as follows why, in the composition of this inventionprepared from polyethylene and ethylene-base copolymer, the proportionof polyethylene is defined to range between 10 and 75 percent by weightand the proportion of ethylene-base copolymer is defined to rangebetween 90 to 25 percent by weight with a sum of the proportions of bothcomponents taken to be 100 parts by weight. Where the content ofpolyethylene falls below 10 percent by weight, the resultant productdoes not retain substantially the same degree of heat resistance aspolyethylene. When, therefore, heated to about 90° to 100° C., thesample fails to hold its original form due to thermal softening. In thecombustion test, the sample readily gives rise to dimensional changesand melt dripping, thus indicating drawbacks in respect of combustionbehavior or flame retardancy. Where the content of polyethyleneincreases over 75 percent by weight, the resultant product exceedinglydecreases in extensibility.

An ethylene-α-olefin copolymer in which the light absorption coefficientK'770 cm⁻¹ is determined to range between 7 and 15 represents the typeof low crystallinity which contains less than 20 percent by weight ofα-olefins except for propylene. Concrete types of saidethylene-α-olefins are given in the later described examples.

Where an ethylene-base copolymer used with the previously definedpolyethylene is formed of particularly an ethylene-vinyl acetatecopolymer or, for example, that type of the above-describedethylene-α-olefin copolymer in which the light absorption coefficientK'770 cm⁻¹ is determined to range from 7 to 15, then the former caseensures the production of a composition having an excellent flameretardancy as measured by an oxygen index. The latter case can beexpected to provide a composition which shows little tendency toward adecline in the mechanical properties which might result from addition ofpowders of an inorganic material at high concentration.

Where a composition is formed of 100 parts by weight of a resincomponent prepared from 25 to 60 parts by weight of an ethylene-vinylacetate copolymer containing 10 to 75 percent by weight of vinyl acetateand 75 to 40 parts by weight of polyethylene, and 80 to 250 parts ofpowders of a hydrated metal oxide as measured on the basis of 100 partsby weight of the above-mentioned composition, then said compositiondisplays an appreciably larger oxygen index than that which is obtainedby simply arithmetically adding together the oxygen index of acomposition prepared from the ethylene-vinyl acetate copolymer and thepowder of hydrated metal oxide and the oxygen index of a compositionprepared from the polyethylene and the powder of hydrated metal oxide.The composition of this invention prepared from particularly 55 to 40parts by weight of an ethylene-vinyl acetate copolymer and hydratedmetal oxide shows a larger oxygen index than when said subjectcomposition might be formed of the ethylene-vinyl acetate copolymeralone.

A hydrated metal oxide used in this invention is a compound which isexpressed by the general structural formula M_(m) O_(n), XH₂ O (where mand n are larger integers than 1 determined by the valence of a metalincluded in the above-mentioned metal oxide), and whose decomposition iscommenced at a temperature ranging from 150° to 450° C., or a doublesalt containing said compound. The hydrated metal oxide concretelyincludes, for example, aluminum hydroxide (Al₂ O₃.3H₂ or Al(OH)₃),magnesium hydroxide (MgO.H₂ O or Mg(OH)₂), calcium hydroxide (CaO.H₂ Oor Ca(OH)₂), barium hydroxide (BaO.H₂ O or BaO.9H₂ O), hydrate ofzirconium oxide (ZrO.nH₂ O), hydrate of stannous oxide (SnO.nH₂ O),basic magnesium carbonate (3MgCO₃.Mg(OH)₂.3H₂ O), hydrotalcite (6MgO.Al₂O₃.H₂ O), dawsonite (NaCO₃.Al₂ O₃.nH₂ O), and borax (Na₂ O.B₂ O₃.5H₂ O).

The temperature at which the resin used in this invention is thermallydecomposed falls within the range of temperature in which a hydratedmetal oxide begins to be decomposed. The above-mentioned coincidencebetween both decomposition temperatures greatly contributes to the flameretardancy of the subject composition due to the effective expellationof bound water, the dilution of said composition resulting fromvaporization and heat absorption. It is also possible to carry out thethermal decomposition in a plurality of stages by adding more than twokinds of the aforesaid hydrated metal oxide. Aluminum hydroxide andmagnesium hydroxide having an excellent effect and capable of beingproduced at a relatively low cost is most favorably accepted.

For the object of this invention, the hydrated metal oxide is applied inthe form of powder, whose average particle size generally ranges between0.01 to 30 microns, preferably from 0.05 to 10 microns, or morepreferably 0.1 to 2.0 microns. Where the particle size exceeds theabove-mentioned range, then a molded product will undesirably have aroughened surface, decline in mechanical strength and decrease in flameretardancy. Where the particle size falls below 0.01 microns, then theimprovement of the tensile property of the resultant product by additionof a surface-treating agent will be reduced. For the object of thisinvention, it is possible to apply a hydrated metal oxide such asdawsonite which is obtained in the form of fibers.

With this invention, the content of the hydrated metal oxide is chosento range between 80 and 250 parts by weight on the basis of 100 parts byweight of resin component. Where the content of the hydrated metal oxidedoes not reach the lower limit, then the resultant composition will notbe rendered so highly flame-retardant as is ensured in this invention.Where the content of the hydrated metal oxide rises above the upperlimit, then the resultant product will be too much reduced in mechanicalproperty for practical application.

If the surface of the powder of an inorganic material used in thisinvention is previously treated with a titanate base coupling agent,then the resultant product will be noticeably improved in extensibility.

This titanate base coupling agent will later be detailed. Nowdescription is given of, for example, isopropyl-triisostearoyl-titanateexpressed by the following structural formula: ##STR1##

The isopropyl radical reacts with the hydroxy radical deposited on thesurface of the powder of an inorganic material to expel isopropylalcohol. At this time, the surface of the powder of the inorganicmaterial and an atom of titanium are bonded together by means of an atomof oxygen, causing the surface of the powder of the inorganic materialto be coated with the stearoyl radical. This stearoyl radical issupposed to be compatible with the matrix-forming molecular chain of apolymer and physically entangled or chemically bonded therewith. It isnot yet clearly defined why the treatment of the surface of the powderof the inorganic material by the above-mentioned titanate base couplingagent prominently improves the extensibility a polyethylene resincomposition containing a large amount of an inorganic material. However,said increased extensibility is assumed to result not only from theelevated dispersibility of the powder of the inorganic material by thetitanate base coupling agent, but also from favorable interactionbetween a hydrocarbon radical having a relatively large number of carbonatoms and a long chain like that which is included, for example, in thestearoyl radical, and a short chain branch included in a polymer.

The titanate base compound is monoalkoxy organic titanate, and includesisopropyl-triisostearoyl-titanate,isopropyl-isostearoyl-dimethacryl-titanate,isopropyl-isostearoyl-diallyl-titanate, isopropyl-tri(dioctylphosphate)titanate, and isopropyl-tri(dioctyl-pyrophosphate) titanate.Particularly preferred among the above-listed titanate base compounds ismonoalkoxy isopropyl-triisostearoyl titanate which has a saturatedaliphatic acid radical, is readily handled and very much compatible withpolyolefins, and prominently improves the extensibility of the subjectcomposition. The content of this last mentioned titanate base compoundis chosen to range between 0.1 and 10, or preferably 0.5 and 7 parts byweight on the basis of 100 parts by weight of the inorganic material. Itis preferred to carry out the pretreatment of the surface of the powderof the inorganic material, because it enables the subsequent full-scaletreatment by the titanate base compound to be undertaken efficiently andat low cost. However, it is possible to add the powder of the inorganicmaterial polyolefins and apply said titanate base compound when themixture is kneaded.

Powder of a hydrated metal oxide whose surface is treated with thetitanate base compound should be applied in an amount ranging between100 and 250, preferably 100 and 200 parts by weight on the basis of 100parts by weight of a resin component. This is because the addition ofsaid surface-treated hydrated metal oxide powder falling within theabove-specified range prominently improves the extensibility of theresultant composition.

It is desired to use the ordinary lubricant in order to elevate theworkability of a composition embodying this invention. Particularlypreferred is the lubricant whose composition is expressed by thefollowing structural formula: ##STR2## where:

R=alkyl radical having 4 to 22 carbon atoms

A=OH, NH₂, alkyloxy radical having 1 to 22 carbon atoms or alkenyloxyradical

N=metal atoms belonging to Groups Ia, IIa, IIb, IIIa, IIIb, IVa and IVbof the periodic table

n=a positive integer corresponding to the valence of a metal

Joint use of saturated aliphatic acid having 4 to 22 carbon atoms,esters, amides or metal salts thereof and the titante base compoundnoticeably increases the workability and mechanical property such asextensibility of the resultant composition.

Saturated aliphatic acids having 4 to 22 carbon atoms, esters, amidesand metal salts thereof are known to be effective by themselves islubricants for polyolefins. Where, however used alone for thecomposition of this invention, such lubricants fail to display as muchsatisfactory effect as expected. Therefore, it is assumed that some kindof interaction arises between the aliphatic acid radical contained inthe lubricants and titanate base compounds, giving rise to changes inthe cohesive condition of the polymer phase at an interface between saidpolymer and hydrated metal oxide.

The saturated aliphatic acid which has 4 to 22 carbon atoms and whosecomposition is expressed by the aforesaid structural formula, and metalsalts, esters and amides thereof include salts of metals such as Na, Al,Zn and Sn of stearic acid, isostearic acid, lactic acid, capric acid,caproic acid, lauric acid, and oleic acid. Esters of the above-mentionedaliphatic acids include vinylstearate, and n-butyl stearate. Amides ofsaid aliphatic acids include amide stearate, amide oxystearate, amideoleate, and amide ricinoleate. The content of the saturated aliphaticacid having 4 to 22 carbon atoms, and metal salts ester and amidesthereof is chosen to range between 0.5 and 10 parts by weight on thebasis of 100 parts of the whole resin component. Where theabove-mentioned content falls below the lower limit, then it isimpossible to suppress the adhesivity of the kneaded mass to a kneader.Where the content increases over the upper limit, then the kneaded massbecomes exceedingly slippery, rather obstructing the uniform dispersionof a filler in a resin.

The composition of this invention may be mixed with, for example, anultraviolet ray absorbent, antioxidant, copper toxicity inhibitor,antistatic agent, coloring matter, plasticizer, dispersant,cross-linking agent, cross-linking subagent and foaming agent. Further,subject composition may be cross-linked by emission of ionizingradiation such as electrons.

The component of the composition according to this invention are mixedby a double roll mill, Banbury type mixer, a kneader, an extruder or thelike. The composition is then shaped to form a film, a sheet, a board, apipe, etc. by generally used plastic fabrication such as extrusion,calendaring and injection moulding. The film or sheet may further byorientated either uniaxially or biaxially, thus forming a tape. Further,a foaming agent may be added to the composition, so that the compositionin the form of a sheet can be linked by proper method and can then befoamed when heated, while maintaining its gel fraction at 40 to 80%.

It is not desirable that the compositions be heated to 200° C. or moreduring the mixing of the components. If the composition is heated tosuch a high temperature, the hydrated metal oxide will inevitablydehydrated. Preferably, the temperature of the composition should be180° C. or less.

Now referring to some examples, the present invention will be describedmore in detail.

EXAMPLES 1-5, CONTROLS 1-3

Such compositions as listed in the following Table 1 were prepared. Eachcomposition consisted of 60 parts by weight of polyethylene havingspecific density and melt index, 40 parts by weight of ethylenevinylacetate copolymer containing 25 percent by weight of vinyl acetate(trade name: Evaflex EV360, manufactured by Mitsui PolychemicalKabushiki Kaisha) and 100 parts by weight of, as hydrated metal oxide,aluminium hydroxide (trade name: Hydilite H-42M, mean particle size1.0μ, manufactured by Showa Denko Kabushiki Kaisha). These compositionshad been prepared by thoroughly mixing the components in a double rollmill, while maintaining each component at 148° C. The compositions werethen hot-pressed at 145° C., thus providing sheets 1 mm thick. Out ofthese sheets JIS No. 3 dumbbell-shaped test pieces were punched. Thetest pieces were subjected to a tensile strength test specified by Item16, JIS C 3005-1977 "The method testing electric wires insulated byplastics", whereby their elongation and strength were measured. Further,the compositions were shaped into sheets 3 mm thick. Out of these sheetsother test pieces were punched. Using these test pieces, the oxygenindices of the compositions were detected by JIS K 7201-1976 "Combustiontest method of polymers by the oxygen index method". Still further,dumbbell-shaped test pieces were punched out of the sheets of thecompositions. The dumbbell-shaped test pieces thus made were supportedat one end and placed in a hot air bath of 100° C. for 48 hours to seehow they would be deformed by heat. Moreover, to evaluate how easy ordifficult it had been to mix the components of each composition in thedouble roll mill, it was observed how much of the composition adhered tothe rolls of the mill.

The results of the above-mentioned tests and observation were as shownin Table 1. The polymers used are as follows:

Example 1: Sholex S4002B (manufactured by Showa Sekiyu Kabushiki Kaisha)

Example 2: Sholex S4002E (manufactured by Showa Sekiyu Kabushiki Kaisha)

Example 3: Neozex 2006H (manufactured by Mitsui Sekiyu Kagaku KogyoKabushiki Kaisha)

Example 4: Yukalon YF-30 (manufactured by Mitsubishi Yuka KabushikiKaisha)

Example 5: NUC-9025 (manufactured by Nippon Unicar Kabushiki Kaisha)

Control 1: Hyzex 3300F (manufactured by Mitsui Sekiyu Kagaku KogyoKabushiki Kaisha)

Control 2: Sholex F6050V (manufactured by Showa Denko Kabushiki Kaisha)

Control 3: Yukalon YK-30 (manufactured by Mitsubishi Yuka KabushikiKaisha)

The values of K'770 given in Table 1 were recorded from the infraredspectrum of film-like test pieces in such manner as described in thepresent specification.

As clearly understood from Table 1, only those compositions whose basepolymer, i.e. polyethylene, had specified density and MI exhibited ahigh elongation (350% or more) and other excellent properties.

                  TABLE 1                                                         ______________________________________                                        Examples 1-5                                                                         E. 1 E. 2   E. 3   E. 4 E. 5 C. 1 C. 2 C. 3                            ______________________________________                                        Polyethylene                                                                           60     60     60   60   60   60   60   60                            Density                                                                       (g/cm.sup.3)                                                                           0.940  0.935  0.922                                                                              0.920                                                                              0.918                                                                              0.954                                                                              0.960                                                                              0.920                         MI                                                                            (g/10 min)                                                                             0.20   0.20   0.7  1.0  2.0  1.2  6.0  4.0                           K'770    1.07   1.10   4.05 1.01 0.93 1.31 0    1.03                          EVA      40     40     40   40   40   40   40   40                            Hydrated                                                                      metal oxide                                                                   Al(OH).sub.3                                                                           100    100    100  100  100  100  100  100                           Elongation                                                                    (%)      565    498    586  510  580  268  75   230                           Tensile                                                                       strength                                                                      (kg/cm.sup.2)                                                                          128    120    131  117  125  110  135  78                            Oxygen index                                                                  (%)      27     27     27   27   26   27   26   27                            Heat                                                                          resistance*.sup.1                                                                      °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                                                                           °                                                                           x                             Workability*.sup.2                                                                     °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           x    x    °                      ______________________________________                                         Note:                                                                         *.sup.1 Mark "°" denotes those which underwent thermal deformation     of 5% or less, and mark "x" those which underwent thermal deformation of      more than 5%.                                                                 *.sup.2 Mark "x"  denotes those which adhered to the rolls so firmly that     the sheets could not easily be peeled off, and mark "°" those whic     could easily peeled off.                                                 

EXAMPLES 6-9, CONTROLS 4-7

Such compositions as listed in the following Table 2 were prepared. Eachof these compositions consisted of 50 parts by weight of polyethylenehaving a density of 0.922 g/cm³ and a melt index of 0.7 (trade name:Neozex 2006H, manufactured by Mitsui Sekiyu Kagaku Kogyo KabushikiKaisha), 50 parts by weight of an ethylene series copolymer and 150parts by weight of, as hydrated metal oxide, aluminium hydroxide powder(trade name: Hydilite H-42M, manufactured by Showa Denko KabushikiKaisha). The compositions had been prepared by thoroughly mixing thecompounds in a mixing unit of Brabender Plastograph. Using the resultantmixture, test pieces were made in the same way as in Example 1. The testpieces were subjected to various test similar to those carried out inExample 1, thus evaluating their properties. The results were as shownin Table 2. All the products of Examples 6-9 exhibited a high elongationand a large oxygen index, though containing a large amount of aninorganic material.

The ethylene series copolymers used are as follows:

Example 6: Ethylene-vinyl acetate copolymer (EVA), Evaflex EV360,containing 25 percent by weight of vinyl acetate (manufactured by MitsuiPolychemical Kabushiki Kaisha)

Example 7: Ethylene-vinyl acrylate copolymer (EEA), DPDJ-6182,containing 15 percent by weight of ethyl acrylate (manufactured byMitsui Polychemical Kabushiki Kaisha)

Example 8: Ethylene-propylene rubber (EPR), EP-07-P, containingpropylene (manufactured by Mitsui Sekiyu Kagaku Kogyo Kabushiki Kaisha)

Example 9: Ethylene-α-olefin copolymer, Toughmer-4085, K'770=11.08(manufactured by Mitsui Sekiyu Kagaku Kogyo Kabushiki Kaisha)

                  TABLE 2                                                         ______________________________________                                        Examples 6-9, Controls 4-7                                                           E. 6 E. 7   E. 8   E. 9 C. 4*                                                                              C. 5 C. 6 C. 7                            ______________________________________                                        Polyethylene                                                                           50     50     50   50   100                                          Density                                                                       (g/cm.sup.3)                                                                  0.922                                                                         MI                                                                            (g/10 min)                                                                    0.7                                                                           K'770 = 4.05                                                                  EVA      50                           100                                     EEA             50                         100                                EPR                    50                       100                           Ethylene-                                                                     α-olefin                                                                copolymer                   50                                                Hydrated                                                                      metal                                                                         oxide                                                                         Al(OH).sub.3                                                                           150    150    150  150  150  150  150  150                           Elongation                                                                    (%)      460    440    635  550  35   560  480  1150                          Tensile                                                                       strength                                                                      (kg/cm.sup.2)                                                                          77     65     55   90   56   120  86   36                            Oxygen                                                                        index (%)                                                                              35     32     28   29   28   36   31   28                            Heat                                                                          resistance                                                                             °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           x    x    x                             Workability**                                                                          °                                                                             °                                                                             °                                                                           °                                                                           x    x    x    x                             ______________________________________                                         Note:                                                                         *The composition of Control 4 did not become homogeneous until the            components were mixed three times.                                            **"x" denotes those which adhered much to the inner wall of the mixing        unit, and "°" denotes those which caused no particular trouble.   

EXAMPLES 10-11, CONTROLS 8-10

Compositions were prepared, each consisting 20 parts by weight ofpolyethylene having a density of 0.935 g/cm³ and MI of 0.2 andK'770=1.10 (trade name: Sholex S4002E, manufactured by Showa YukaKabushiki Kaisha), 80 parts by weight of ethylene-vinyl acetatecopolymer containing 25 percent by weight of vinyl acetate (trade name:Evaflex EV360, manufactured by Mitsui Polychemical Kabushiki Kaisha) and100 parts by weight of powder of an inorganic material. These componentswere mixed and shaped in the same way as in Example 1. The properties ofthese compositions were evaluated. The results were as shown in Table 3.

The inorganic material powders used are as follows:

Aluminium hydroxide: Trade name Hydilite H-42M (manufactured by ShowaDenko Kabushiki Kaisha)

Magnesium hydroxide: Manufactured by Kamishima Kagaku Kabushiki Kaisha

Calcium carbonate: Whiteton SSB, manufactured by Shiraishi Calcium KogyoKabushiki Kaisha

Hard clay: Dixie clay, manufactured by Vanderbilt, Inc.

Talc: Talc MS, manufactured by Nippon Talc Kabushiki Kaisha

As evident from Table 3, the compositions showed sufficient tensilestrength, heat resistance and workability, whatever inorganic materialthey contained. But those containing aluminium hydroxide and magnesiumhydroxide exhibited an oxygen index far larger than those of thecompositions which contained calcium carbonate, hard clay and talc.Table 3 also shows the condition of ashes, i.e. the residue of forcedcombustion of the test pieces used for evaluating oxygen index, by meansof a methane gas burner. Calcium carbonate and talc lost their originalform in natural manner. The ashes of the hydroxides, which areself-cohesive, held the original form of the hydroxides. When exertedwith external force, they collapsed.

                  TABLE 3                                                         ______________________________________                                        Examples 10-11, Controls 8-10                                                           E. 10 E. 11   C. 8    C. 9  C. 10                                   ______________________________________                                        Polyethylene                                                                              20      20      20    20    20                                    Density (g/cm.sup.3)                                                          0.935                                                                         MI (g/10 min)                                                                 0.2                                                                           K'770 = 1.10                                                                  EVA         80      80      80    80    80                                    Aluminium                                                                     hydroxide   100                                                               Magnesium                                                                     hydroxide           100                                                       Calcium carbonate           100                                               Hard clay                         100                                         Talc                                    100                                   Elongation (%)                                                                            565     540     470   440   490                                   Tensile strength                                                              (kg/cm.sup.2)                                                                             130     135     148   151   147                                   Oxygen index (%)                                                                          28      28      23    24    23                                    Heat resistance                                                                           °                                                                              °                                                                              °                                                                            °                                                                            °                              Workability °                                                                              °                                                                              °                                                                            °                                                                            °                                                      Holding no                                            Condition of ashes                                                                        Self-cohesive                                                                             original form                                         ______________________________________                                    

EXAMPLES 12-15, CONTROLS 10-12

Polyethylene having a density of 0.940 g/cm³, MI of 0.2 and K'770=1.07(trade name: Sholex 4002B, manufactured by Showa Yuka Kabushiki Kaisha),ethylenevinyl acetate copolymer containing 25 percent by weight of vinylacetate and having a density of 0.94 g/cm³ and MI of 2.0, thepolyethylene and copolymer being used in such amount as shown in Table4, and 100 parts by weight of powder of aluminium hydroxide (trade name:Hydilite H-42M, manufactured by Showa Denko Kabushiki Kaisha) with a sumof the polyethylene and copolymer taken to be 100 parts by weight weremixed, thus preparing compositions. The compositions were tested in thesame way as that of Example 1. The results of the test were as shown inTable 4. The composition containing 80 or more parts by weight ofpolyethylene had an elongation far less than 350% and, in addition,adhered to the rolls as that the components could not mixed smoothly.The composition containing no polyethylene had an insufficient heatresistance and, in addition, adhered to the rolls and had a poorworkability. By contrast, the compositions containing 20 to 60 parts byweight of polyethylene exhibited an elongation well over 350%, a highheat resistance, a good workability. Surprisingly, they had an extremelylarge oxygen index. Obviously they proved excellent in flame retardancy.

As proved by Examples 12 and 13, where ethylenevinyl acetate copolymeris used in an amount of less than 60 parts by weight and more than 20parts by weight, the composition tends to have its oxygen indexparticularly elevated.

                  TABLE 4                                                         ______________________________________                                        Example 12-15, Controls 10-12                                                           C. 10                                                                              C. 11  E. 12  E. 13                                                                              E. 14                                                                              E. 15                                                                              C. 12                             ______________________________________                                        Polyethylene                                                                              100    80     60   45   40   20   0                               Density (g/cm.sup.3)                                                          0.940                                                                         MI (g/10 min)                                                                 0.2                                                                           K'770 = 1.07                                                                  EVA         0      20     40   55   60   80   100                             Hydrated metal                                                                            100    100    100  100  100  100  100                             oxide Al(OH).sub.3                                                            Elongation (%)                                                                            40     120    410  555  565  590  650                             Tensile strength                                                                          50     85     95   125  128  131  155                             (kg/cm.sup.2)                                                                 Oxygen index (%)                                                                          24     25     30   32   27   28   29                              Heat resistance                                                                           °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                                                                           x                               Workability x      x      °                                                                           °                                                                           °                                                                           °                                                                           x                               ______________________________________                                    

EXAMPLES 16-20

30 parts by weight of polyethylene having a density of 0.940 g/cm³ andMI of 0.2 g/min (trade name: Sholex 4002B, manufactured by Showa YukaKabushiki Kaisha), 70 parts by weight of, as an ethylene-base copolymer,ethylene-α-olefin copolymer having a density of 0.89 g/cm³ and MI of 0.2(trade name: Toughmer A-4090, manufactured by Mitsui Yuka Kagaku KogyoKabushiki Kaisha) and 100 to 200 parts by weight of powder of aluminiumhydroxide (trade name: Hydilite H-42M, manufactured by Showa DenkoKabushiki Kaisha) were mixed to form such compositions as shown in thefollowing Table 5. The products were tested in the same way as that ofExample 6. The results were as shown also in Table 5. Even thecomposition containing 200 parts by weight of powder of aluminiumhydroxide had an elongation of 350% or more. The compositions obtainedexhibited good characteristics.

                  TABLE 5                                                         ______________________________________                                        Examples 16-20                                                                              E. 16                                                                              E. 17  E. 18  E. 19                                                                              E. 20                                   ______________________________________                                        Polyethylene    30     30     30   30   30                                    Ethylene-α-                                                             olefin copolymer                                                                              70     70     70   70   70                                    (K'770 = 7.53)                                                                Hydrated metal                                                                oxide Al(OH).sub.3                                                                            100    120    150  170  200                                   Elongation (%)  640    620    580  520  390                                   Tensile strength                                                              (kg/cm.sup.2)   133    120    105  90   58                                    Oxygen index (%)                                                                              25     27     29   30   32                                    Heat resistance °                                                                             °                                                                             °                                                                           °                                                                           °                              Workability     °                                                                             °                                                                             °                                                                           °                                                                           °                              ______________________________________                                    

EXAMPLES 21-27

15 parts by weight of polyethylene having a density of 0.935 g/cm³ andMI of 0.20 (trade name: Sholex S4002E, manufactured by Showa YukaKabushiki Kaisha), 85 parts by weight of ethylene-vinyl acetatecopolymer containing 25 percent by weight of vinyl acetate, 100 to 170parts by weight of powder of aluminium hydroxide (trade name: HydiliteH-42M, manufactured by Showa Denko Kabushiki Kaisha) with the resinconsisting of the polyethylene and copolymer taken to be 100 parts byweight, 3 parts by weight of, as titanate series compound,isopropyl-triisostearoyl titanate (trade name: KENREACT TTS,manufactured by Kenrich Petrochemical, Inc.) with the powder ofaluminium hydroxide taken to be 100 parts by weight and 1 parts byweight of zinc stearate (1st-grade reagent) with the resin taken to be100 parts by weight were mixed to form compositions. The compositionswere tested in the same way as that of Example 6. The composition ofExample 26 contained no zinc stearate, and the composition of Example 27contained neither zinc stearate nor the titanate series compound. Theresults of the test were as shown in the following Table 6.

As evident from Table 6, all the compositions listed therein exhibitedan elongation of 350% or more, a large oxygen index, a high heatresistance and an excellent workability. Particularly, the elongationwas improved by addition of aforesaid titanate series compound. Further,the elongation was further promoted by using zinc stearate, i.e. a fattyacid series compound, which is represented by the following generalformula: ##STR3## where R=C₄ -C₂₂ alkyl group, A=OH, HN₂, a C₁ -C₂₂alkyloxy group or alkenyloxy group, M=metal atoms of Groups Ia, IIa,IIb, IIIa, IIIb, IVa and IVb of the periodic table, and n=a positiveinteger corresponding to the valence of metal.

Still further, the compositions did not adhere to the inner surfaces ofthe mixing unit of Brabender Plastograph, and thus proved to have theirworkability improved very much.

                  TABLE 6                                                         ______________________________________                                        Examples 21-27                                                                          E. 21                                                                              E. 22  E. 23  E. 24                                                                              E. 25                                                                              E. 26                                                                              E. 27                             ______________________________________                                        Polyethylene                                                                              15     15     15   15   15   15   15                              Density (g/cm.sup.3)                                                          0.94                                                                          MI (g/10 min.)                                                                0.20                                                                          K'770 = 1.07                                                                  EVA         85     85     85   85   85   85   85                              Aluminium   80     100    120  150  170  150  150                             hydroxide                                                                     Surface treat-                                                                            2.4    3.0    3.6  4.5  5.1  4.5  0                               ment agent                                                                    Zinc stearate                                                                             0      1      1    1    1    0    0                               Elongation (%)                                                                            660    658    592  525  350  490  440                             Tensile strength                                                                          130    128    95   84   50   76   80                              (kg/cm.sup.2)                                                                 Oxygen index (%)                                                                          25     28     31   35   38   35   35                              Heat resistance                                                                           °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                                                                           °                        Workability °                                                                             ⊚                                                                     ⊚                                                                   ⊚                                                                   °                                                                           °                                                                           °                        ______________________________________                                    

EXAMPLES 28-36

50 parts by weight of ethylene-vinyl acetate copolymer containing 25percent by weight of vinyl acetate (trade name: Evaflex EV360 having amelt index of 0.2, manufactured by Mitsui Polychemical KabushikiKaisha), 50 parts by weight of medium pressure polyethylene (trade name:Neozex 2006H, density of 0.922 g/cm³, →melt index of 0.7, manufacturedby Mitsui Sekiyu Kagaku Kobyo Kabushiki Kaisha) and 100, 150 or 200parts by weight of powder of aluminium hydroxide (trade name: HydiliteH-32, mean particle size of 3.5μ, manufactured by Showa Denko KabushikiKaisha) were mixed to form compositions in the same way as that ofExample 6. The oxygen index of each of these compositions was measuredin the same way as was that of the composition of Example 1. Out of thesheets of these compositions, all 1 mm thick, dumbbell-shaped testpieces were punched. The test pieces were subjected to the testspecified by Item 16, JIS C 3005-1977 "The method testing electric wiresinsulated by plastics", whereby their tensile strength and elongation atbreak were measured. The results of the test were as shown in thefollowing Table 7.

Other compositions were prepared, which were identical with thosementioned in the preceding paragraph, except that the powder ofaluminium hydroxide were preliminarily surface-treated withisopropyl-triisostearoyl titanate used in an amount of 5 parts by weightwith the powder of aluminium hydroxide taken to be 100 parts by weight.The same test was conducted on these compositions.

Still further, other compositions were prepared, which were identicalwith those mentioned in the preceding paragraph, except that, inaddition to the surface treatment of the powder of aluminium hydroxidewith isopropyl-triisostearoyl titanate, zinc stearate was added in anamount of 1.5 parts by weight with all the resin taken to be 100 partsby weight. The same test was conducted on these compositions, too. Theresults of the test were as shown in Table 7.

As evident from Table 7, isopropyl-triisostearoyl titanate used as asurface treatment agent did not affect the oxygen index at all. Theoxygen index was not affected when zinc stearate was added to thiscompound. The compositions containing powder of aluminium hydroxidesurface-treated with isopropyl-triisostearoyl titanate had their tensilestrength and other properties improved far more than the compositionscontaining powder of aluminium hydroxide not surface treated. Thetensile strength and other properties were further improved when zincstearate was used together with isopropyl-triisostearoyl titanate, asevident from Table 7.

To evaluate the mixing workability of each composition, a Banbury typemixer was used, and the components of each composition were mixed, whilemaintaining the resin at 156° C. The compositions which containedisopropyl-triisostearoyl titanate and zinc stearate proved to have agood workability in comparison with the other compositions. That is, thewhole composition could be taken out of the Banbury type mixer in asingle dump-out. By contrast, any one of the other compositions adheredto the inner surfaces of the Banbury type mixer, and the entirecomposition could not be taken out from the mixer in a single dump-outin many cases.

                                      TABLE 7                                     __________________________________________________________________________          Aluminium                                                                           Isopropyl-                                                                           Zinc                                                             hydroxide                                                                           triisostearoyl                                                                       stearate                                                                           Oxygen                                                                             Tensile                                                                            Elongation                                        (parts by                                                                           titanate (parts                                                                      (parts by                                                                          index                                                                              strength                                                                           at (break                                   No.   weight)                                                                             by weight)                                                                           weight)                                                                            (%)  (kg/cm.sup.2)                                                                      (%)                                         __________________________________________________________________________    Example 28                                                                          100   --     --   31   103  550                                         29    100   5      --   31   105  660                                         30    100   5      1.5  31   102  720                                         31    150   --     --   38   85   360                                         32    150   5      --   38   103  410                                         33    150   5      1.5  38   99   500                                         34    200   --     --   44   78   210                                         35    200   5      --   44   85   330                                         36    200   5      1.5  44   93   400                                         __________________________________________________________________________

EXAMPLES 37-38, CONTROLS 13-14

60 parts by weight of polyethylene having a density of 0.920 g/cm³, amelt index of 1.5 and K'770=2.87 (trade name: Neozex 2015M, manufacturedby Mitsui Yuka Kagaku Kogyo Kabushiki Kaisha), 40 parts by weight ofethylene-vinyl acetate copolymer containing 19 percent by weight ofvinyl acetate and having a density of 0.94 g/cm³ and a melt index of 2.5(trade name: Evaflex EV460, manufactured by Mitsui PolychemicalKabushiki Kaisha), a surface treatment agent consisting of titanateseries compound, i.e. isopropyl-dimethacrylisostearoyl titanate (tradename: KENREACT TSM2-7, manufactured by Kenrich Petrochemical, Inc.) andpowder of aluminium hydroxide (trade name: Hydilite H-32, manufacturedby Showa Denko Kabushiki Kaisha) were mixed to from compositions in thesame way as the composition of Example 1, the surface treatment agentand the powder of aluminium hydroxide being used in such amount as shownin the following Table 8. The powder of aluminium hydroxide had beenpreliminarily surface-treated with the titanate series compound, using ahigh-speed stirring mill for use in laboratory.

Other compositions (hereinafter called "Controls 13 and 14) wereprepared, which were to be compared with the compositions stated in thepreceding paragraph and which were identical with said compositionsexcept that use was made of a silane series (coupling agent, i.e.vinyl-tri(2-methoxyethoxy) silane (trade name: A-172, manufactured byNippon Unicar Kabushiki Kaisha) in such an amount as shown in Table 8.Also in this case the silane compound was diluted with an aqueoussolution of alcohol and then was used to treat the surface of aluminiumhydroxide, using the above-mentioned high-speed stirring mill.

Both Examples 37 and 38 and both Controls 13 and 14 were subjected totensile strength test. The results of the test were as shown in Table 8.Table 8 proves that the titanate series compound, unlike silane seriescoupling agent, provided the composition with a high elongation.

                  TABLE 8                                                         ______________________________________                                                             Alumin-                                                                       ium    Surface                                                                hydrox-                                                                              treatment                                                              ide    agent   Elon- Tensile                                                  parts by                                                                             parts by                                                                              gation                                                                              strength                            No.   PE     EVA     weight weight  (%)   (kg/cm.sup.2)                       ______________________________________                                        Exam-                                                                         ple 37                                                                              60     40      100    TSM2-7:2                                                                              550   85                                  Exam-                                                                         ple 38                                                                              60     40      150    TSM2-7:3                                                                              400   73                                  Con-                                                                          trol 13                                                                             60     40      100    A-72:2  215   58                                  Con-                                                                          trol 14                                                                             60     40      150    A-72:3   50   30                                  ______________________________________                                    

EXAMPLE 39, CONTROLS 15-17

A medium pressure, highly dense polyethylene, ethylene-vinyl acetatecopolymer, powder of aluminium hydroxide, a titanate compound,azodicarbonamide, i.e. foaming agent, and dicumyl peroxide, i.e. linkingagent were used in such amounts as shown in the following Table 9 andwere mixed in a double roll mill, the surface temperature of which wasmaintained at 140° C., thus preparing some compositions. Thecompositions were hot-pressed to form sheets each 3 mm thick. From thesesheets there were cut strips 3 cm by 3 cm. The strips were each wrappedup in an aluminium foil and were then immersed in the Wood's alloy bathof 200° C. for 10 minutes. They were taken out of the bath and cooled.

The bulk density of the samples of foamed compositions was measured, andthe bubble size thereof was recorded. The results were as set forth alsoin Table 9.

The sample of the composition according to this invention had the lowestbulk density and a uniform bubble size. (The amount of the linkingagent, DCP, had been already selected and was such that each compositionmight have the lowest possible bulk density.)

                  TABLE 9                                                         ______________________________________                                                   E. 39  C. 15    C. 16    C. 17                                     ______________________________________                                        (Composition) (Parts                                                          by weight)                                                                    PE 1, density                                                                 0.935 g/cm.sup.3                                                                           60       --       100    --                                      MI 0.20                                                                       PE 2, density                                                                 0.945 g/cm.sup.3                                                                           --       60       --     --                                      MI 0.25                                                                       EVA          40       40       --     100                                     Al(OH).sub.3 150      150      150    150                                     ADCA         10       10        10     10                                     Titanate compound                                                                          4.5      4.5      4.5    4.5                                     DCP          0.8      0.8      1.0    0.7                                     Density of                                                                    foamed mass (g/cm.sup.3)                                                                   0.08     0.13     0.11   0.24                                    Uniformness of                        Rela-                                   bubble                Large    Large  tively                                                        not      not    not                                                  Uniform  uniform  uniform                                                                              uniform                                 ______________________________________                                         Notes:                                                                        PE 1: Sholex S4002E, manufactured by Showa Yuka Kabushiki Kaisha              PE 2: Sholex S6002, manufactured by the same company as mentioned above       EVA: Evaflex EV360, VA content: 25 weight %, density: 0.95 g/cm.sup.3,        melt index: 2.0, manufactured by Mitsui Polychemical Kabushiki Kaisha         Al(OH).sub.3 : Hydilite H42M, manufactured by Showa Denko Kabushiki Kaish     Titanate compound: TTS, manufactured by Kenrich Petrochemical, Inc.           ADCA: Azodicarbonamide (regent)                                               DCP: Dicumyl peroxide (regent)                                           

EXAMPLE 40

If applied to a fire-resistant cable sheath, the composition of thisexample will bring forth good results.

About a soft cooper wire with a cross section of 3.5 mm², made of finecopper wires twisted together, a glass-mica tape 0.13 mm thick was woundso that each turn overlapped half width of the other. Then, anotherglass-mica tape 0.13 mm thick was wound in the same manner, thusproviding a fire-resistant layer 0.5 mm thick. The fire-resistant layerwas provided with an extruded coating 0.8 mm thick of polyethylenehaving a density of 0.92 g/cm³ and a melt index of 1.0. In this wayinsulated wires were produced. Three insulated wires thus provided weretwisted together with split fiber of polypropylene, thereby providing astrand. About the strand a nylon tape 0.05 mm thick was wound.Thereafter the strand was provided with an extruded coating 1.5 mmthick, whereby a fire-resistant cable was manufactured. The extrudedcoating or sheath was made of a composition which had been prepared bymixing, in a Banbury type mixer, 85 parts by weight of ethylene-vinylacetate copolymer containing 25 percent by weight of vinyl acetate(trade name: Evaflex EV360, manufactured by Mitsui PolychemicalKabushiki Kaisha), 15 parts by weight of polyethylene having a meltindex of 0.2 (trade name: Sholex 4002B, manufactured by Showa DenkoKabushiki Kaisha), 100 parts by weight of powder of aluminium hydroxide(trade name: Hydilite H-42M, manufactured by Showa Denko KabushikiKaisha) and lubricant, coloring agent and stabilizing agent in necessaryamounts. (This composition was similar to Example 22 in respect ofproperties.) The fire-resistant cable thus manufactured had as goodmechanical and thermal properties as those of known fire-resistantcables.

Other fire-resistant cables (i.e. Controls) were manufactured to becompared with the above-mentioned cable, in the same way as was theabove-mentioned cable except that use was made of an extruded coating1.5 mm thick of a soft polyvinyl chloride composition (corresponding toone specified by No. 2, JIS K 6723).

The fire-resistant cables using the composition of this invention andthe other cables were tested in accordance with the fire resistance teststandards which are shown in Table 10. The results of the test were asshown in Table 11. As this table clearly shows, the fire-resistantcables whose sheaths were made of the composition according to thisinvention had fire resistance improved well over that of the sheaths ofthe known cables (i.e. Controls). Moreover, the product of thisinvention emitted almost no black smoke when burnt. Nor did it emithydrochloric acid gas at all.

                  TABLE 10                                                        ______________________________________                                        Standards for testing fire-resistant cables                                                     Test piece must have                                                          insulation resistance of                                                      50 MΩ or more, and must                               Before test       withstand 1,500V/min                                        ______________________________________                                        Heating           Test piece must withstand                                   (Heat the test piece along                                                                      600V.                                                       the fire temp. curve                                                                            It must have insulation                                     JIS A 1340 for 30 min.                                                                          resistance of 0.4 MΩ or                               840° C. at the end of the                                                                more.                                                       30 min. heating)                                                              After test        It must withstand                                                             1,500V/min.                                                 Combustion        It must not be burnt at                                     characteristic    1,500 mm or more from the                                                     inner wall of the furnace                                   ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Results the fire resistance test                                                           Cables                                                                        (Example 40)                                                                             Controls                                                           No.  No.    No.    No.  No.  No.                                              1    2      3      1    2    3                                   ______________________________________                                        Before test    Passed the test                                                                            Passed the test                                   Insulation                                                                    resistance (MΩ)                                                         after 30 min.                                                                 heating        8.0    9.5    9.5  1.2  1.0  2.5                               Insu-   During                                                                lation  heating                                                               with-   600V       Passed the test                                                                            Passed the test                               stand   After                                                                 voltage combustion                                                                    1,500V/                                                                       min.       "            "                                             Com-                                                                          bustion Left:      50     50   50   60   55   55                              charac-                                                                       teristic                                                                              Right:     60     50   50   50   50   50                              (mm)                                                                          Breakdown                                                                     voltage (V)    2,700  2,800  2,850                                                                              1,700                                                                              1,700                                                                              2,000                             ______________________________________                                    

EXAMPLES 41-47, CONTROL 18

Compositions were prepared, each by mixing, in the same way as inExample 6, 50 parts by weight of polyethylene having a density of 0.922g/cm³, MI of 0.7 and K'770=4.05 (trade name: Neozex 2006H, manufacturedby Mitsui Sekiyu Kagaku Kogyo Kabushiki Kaisha), 50 parts by weight ofethylene-vinyl acetate copolymer containing vinyl acetate in such anamount as shown in Table 12 and 100 parts by weight of powder ofaluminium hydroxide (trade name: Hydilite H-42M, manufactured by ShowaDenko Kabushiki Kaisha). The compositions were shaped and tested in thesame way as that of Example 6. The results of the test were as shown inTable 12.

The ethylene-vinyl acetate copolymers used are as follows:

Example 41: DQDJ-1830 (trade name) having a density of 0.93 g/cm³ and MIof 3 (manufactured by Nippon Unicar Kabushiki Kaisha). Example 42:Evaflex EV560 (trade name) having a density of 0.93 g/cm³ and MI of 3.5(manufactured by Mitsui Polychemical Kabushiki Kaisha). Example 43:Evaflex EV460 (trade name) having a density of 0.94 g/cm³ and MI of 2.5(manufactured by Mitsui Polychemical Kabushiki Kaisha). Example 44:Evaflex EV360 (trade name) having a density of 0.95 g/cm³ and MI of 2(manufactured by Mitsui Polychemical Kabushiki Kaisha). Example 45:Evaflex EV260 (trade name) having a density of 0.95 g/cm³ and MI of 6(manufactured by Mitsui Polychemical Kabushiki Kaisha). Example 46:Evaslen 410-P (trade name) having a density of 1.04 g/cm³ and MI of 1 orless (manufactured by Dainippon Ink Kabushiki Kaisha). Example 47:Evaslen 310-P (trade name) having a density of 10.7 g/cm³ and MI of 1 orless (manufactured by Dainippon Ink Kabushiki Kaisha). Control 18:Yukalon YF-30 (trade name) having a density of 0.92 g/cm³ and MI of 1.

As evident from Table 12, the oxygen index increased in proportion tothe content of vinyl acetate as long as the content of vinyl acetate waswithin the range of 10 to 19%. When the content of vinyl acetate wasover 19%, the oxygen index stayed almost unchanged. On the other hand,the elongation and tensile strength were high and good when the contentof vinyl acetate was 19 to 33%. The heat resistance and workability weregood. Thus, it is particularly preferred that use should be made ofethylene-vinyl acetate copolymer containing 15 to 30% of vinyl acetatein order to provide a composition which is highly flame-retardant andwhich has an excellent tensile strength.

                  TABLE 12                                                        ______________________________________                                               E. 41                                                                              E. 42  E. 43  E. 44                                                                              E. 45                                                                              E. 46                                                                              E. 47                                                                              C. 18                           ______________________________________                                        Polyethylene                                                                           50     50     50   50   50   50   50   50                            EVA      50     50     50   50   50   50   50   50                            (VA content                                                                            10     14     19   25   33   60   75   0                             in wt. %)                                                                     Hydrated                                                                      metal oxide                                                                            100    100    100  100  100  100  100  100                           Al(OH).sub.3                                                                  Elongation                                                                             355    440    530  560  560  540  510  8                             (%)                                                                           Tensile                                                                       strength 67     82     97   115  99   76   65   105                           (kg/cm.sup.2)                                                                 Oxygen index                                                                           26     30     32   32   33   32   32   24                            (%)                                                                           Heat     °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                                                                           °                                                                           °                      resistance                                                                    Work-    °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                                                                           °                                                                           °                      ability                                                                       ______________________________________                                    

EXAMPLES 48-50, CONTROLS 19-21

A composition (Example 48) was prepared by mixing, in the same way as inExample 6, 40 parts by weight of the same polyethylene as used inExample 41, 50 parts by weight of ethylene-vinyl acetate copolymercontaining 25 percent by weight of vinyl acetate (trade name: EvaflexEV360, manufactured by Mitsui Polychemical Kabushiki Kaisha), 10 partsby weight of, as a third polymer component, polybutene-1 having adensity of 0.915 g/cm³ (trade name: WITRONO 100, manufactured by WitcoChemical, Inc.) and 100 parts by weight of powder of aluminium hydroxide(trade name: Hydilite H-42M, manufactured by Showa Denko KabushikiKaisha). Another composition (Example 49) was prepared, which wasidentical with Example 48, except that the content of said polyethylenewas reduced to 30 parts by weight and the content of said polybutene-1was increased to 20 parts by weight. Still another composition wasprepared, which was identical with Example 48, except that the thirdpolymer used was polypropylene (trade name: Mitsubishi Noblene MA6,density: 0.90 g/cm³, MI: 1.3, manufactured by Mitsubishi Yuka KabushikiKaisha). Further, compositions containing no polyethylene (Controls19-21) were prepared. All these compositions were tested in the same wayas was the composition of Example 6. The results of the test were asshown in Table 13.

As evident from Table 13, the compositions which contained a smallamount of a third polymer component in addition to the polyethylene andethylene-base copolymer also exhibited a high elongation and a largeoxygen index. By contrast, the compositions which contained onlyethylene-base copolymer and a third polymer component exhibited a farlower elongation.

                  TABLE 13                                                        ______________________________________                                                     E. 48                                                                              E. 49  E. 50  C. 19                                                                              C. 20                                                                              C. 21                               ______________________________________                                        Polyethylene   40     30     40   --   --   --                                Ethylene-vinyl                                                                acetate        50     50     50   50   70   30                                copolymer (EVA)                                                               Third polymer                                                                 1 Polybutene-1 10     20     --   50   30   --                                2 Polypropylene                                                                              --     --     10   --   --   70                                Aluminium      100    100    100  100  100  100                               hydroxide                                                                     Elongation (%) 540    395    525  57   48   32                                Tensile strength                                                                             77     64     68   98   59   120                               (kg/cm.sup.2)                                                                 Oxygen index (%)                                                                             31     32     32   27   27   26                                Heat resistance                                                                              °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                          Workability    °                                                                             °                                                                             °                                                                           °                                                                           °                                                                           °                          ______________________________________                                    

EXAMPLES 51-55

Compositions were prepared, each by mixing, in the same way as inExample 6, 50 parts by weight of polyethylene having a density of 0.490g/cm³, MI of 0.2 and K'770=1.07 (trade name: Sholex 4002B, manufacturedby Showa Denko Kabushiki Kaisha), 50 parts by weight of, asethylene-base copolymer, one selected from such three ethylene-vinylacetate copolymers and two ethylene-propylene-diene terpolymer as shownin Table 14, 150 parts by weight of powder of aluminium hydroxide havingmean particle size of 0.8μ (trade name: Hydilite H-42M, manufactured byShowa Denko Kabushiki Kaisha) and 4.5 parts by weight of, as titanatecompound, isopropyltriisostearoyl titanate (trade name: KENREACT TTS,manufactured by Kenrich Petrochemical, Inc.). These compositions wereshaped and tested in the same way as that of Example 6. Of eachcomposition there were made test pieces, 3.18 mm thick, 12.7 mm wide and127 mm long. The test pieces of the compositions were subjected to acombustion test specified in UL-94 vertical combustion test method. Theresults of the test were as shown in Table 14.

The ethylene-base copolymers used are as follows:

Example 51: Evaflex EV360 (trade name, manufactured by MitsuiPolychemical Kabushiki Kaisha)

Example 52: Evaslen 410-P (trade name, manufactured by Dainippon InkKabushiki Kaisha)

Example 53: Evaslen 310-P (trade name, manufactured by Dainippon InkKabushiki Kaisha)

Example 54: Mitsui EPT #1070 (trade name, manufactured by Mitsui SekiyuKagaku Kabushiki Kaisha)

Example 55: Mitsui EPT #4070 (trade name, manufactured by Mitsui SekiyuKagaku Kabushiki Kaisha)

As shown in Table 14, all the compositions exhibited an oxygen indexover 30. They had good tensile strength and good workability. Of thesecompositions, those which were graded as "V-0" by UL-94 verticalcombustion test method contained ethylene-vinyl acetate copolymercontaining 60 or more percent by weight of vinyl acetate orethylene-propylene-diene copolymer containing, as third component,dicyclopentadiene.

                  TABLE 14                                                        ______________________________________                                                      E. 51                                                                              E. 52  E. 53  E. 54                                                                              E. 55                                   ______________________________________                                        Polyethylene    20     50     50   50   50                                    Ethylene-base                                                                 copolymer                                                                     °EVA 1   50                                                            (VA: 25%)                                                                     °EVA 2          50                                                     (VA: 60%)                                                                     °EVA 3                 50                                              (VA: 75%)                                                                     °EPDM 1                     50                                         (Third component:                                                             DCPD,                                                                         iodine number: 12)                                                            °EPDM 2                          50                                    (Third component:                                                             ethylene                                                                      norbornen                                                                     (ENB), iodine                                                                 number: 24)                                                                   Aluminium       150    150    150  150  150                                   hydroxide                                                                     Elongation (%)  405    390    370  410  395                                   Tensile strength                                                                              67     58     55   49   47                                    (kg/cm.sup.2)                                                                 Oxygen index (%)                                                                              34     36     35   31   30                                    UL-94 vertical  x      V-0    V-0  V-0  x                                     combustion test                                                               Heat resistance °                                                                             °                                                                             °                                                                           °                                                                           °                              Workability     °                                                                             °                                                                             °                                                                           °                                                                           °                              ______________________________________                                         Note:?                                                                        Mark "x" denotes a composition which was not graded V0 to V2 in UL94          vertical combustion test.                                                

EXAMPLES 56-61

Compositions were prepared, each by mixing, in the same way as inExample 6, 20 parts by weight of polyethylene having a density of 0.940g/cm³, MI of 0.2 and K'770=1.07 (trade name: Sholex 4002B, manufacturedby Showa Yuka Kabushiki Kaisha), 80 parts by weight of ethylene-vinylacetate copolymer containing 25 percent by weight of vinyl acetate(trade name: Evaflex EV360, manufactured by Mitsui PolychemicalKabushiki Kaisha), 110 parts by weight of Powder of aluminium hydroxide(trade name: Hydilite H-42M, manufactured by Showa Denko KabushikiKaisha), 11 parts by weight of isopropyl-triisostearoyl titanate (tradename: KENREACT TTS, manufactured by Kenrich Petrochemical, Inc.) and 1part by weight of one of the following fatty acid compounds. Thesecompositions were shaped and tested in the same way as that of Example6.

Example 56: n-caprio acid ##STR4## Example 57: Stearic acid ##STR5##Example 58: Vinyl stearate ##STR6## Example 59: Stearic acid amide##STR7## Example 60: n-butyric acid ##STR8## Example 61: Cerotic acid##STR9##

The results of the test were as shown in Table 15. All the compositionswere excellent in tensile strength, flame retardancy and heatresistance.

The workability of these compositions was evaluated according to theextent to which they adhered to the inner surface of the mixing unit ofBrabender Plastograph. Examples 56-59 had an excellent workability incomparison with Examples 60-61, and it was extremely easy to taken themout of the mixing unit. This means that addition of specific fatty acidcompounds brought out particular effects. The same trend appeared withrespect to elongation and strength.

                  TABLE 15                                                        ______________________________________                                                  E. 56 E. 57   E. 58  E. 59                                                                              E. 60                                                                              E. 61                                ______________________________________                                        Polyethylene                                                                              20      20      20   20   20   20                                 Ethylene-vinyl                                                                acetate                                                                       copolymer   80      80      80   80   80   80                                 Aluminium                                                                     hydroxide   110     110     110  110  110  110                                Titanate-base                                                                 compound    1.1     1.1     1.1  1.1  1.1  1.1                                Fatty acid                                                                    compound                                                                      °n-butyric acid                1                                       °n-caprio acid                                                                     1                                                                 °Stearic acid                                                                              1                                                         °Vinyl stearate      1                                                 °Stearic                                                               acid amide                       1                                            °Cerotic acid                       1                                  Elongation (%)                                                                            595     600     610  620  570  575                                Tensile strength                                                              (kg/cm.sup.2)                                                                             128     125     127  124  116  114                                Oxygen index (%)                                                                          28      28      28   28   28   28                                 Heat resistance                                                                           °                                                                              °                                                                              °                                                                           °                                                                           °                                                                           °                           Workability ⊚                                                                      ⊚                                                                      ⊚                                                                   ⊚                                                                   ⊚                                                                   ⊚                   ______________________________________                                    

INDUSTRIAL APPLICABILITY

As apparent from the foregoing examples, the composition of thisinvention has high extensibility and flame retardancy, and superiorproperties to soft vinyl chloride, thereby meeting social requirementsfor the saving of natural resources and elimination of environmentalpollution, and indicating great industrial merits. Therefore, thesubject composition is favorably accepted as raw material for a field inwhich high flame retardancy is demanded, such as coating of wires andcables and raw material of foamed product which are required to haveprominent flame retardancy.

We claim:
 1. A polyethylene resin composition containing a highconcentration of inorganic materials, characterized in that it mainlyconsists of a resin component formed of (i) 10 to 75 parts by weight ofpolyethylene which has a density ranging from 0.910 to 0.945 g/cm³, anda melt index ranging from 0.01 to 2.0 g/10 min., the value of itsabsorptivity coefficient K'770 of the absorption peak in the proximityof 770 cm⁻¹ in the infrared absorption spectrum, being 0.5 to 6, and(ii) 90 to 25 parts by weight of an ethylene-vinyl acetate copolymer,said composition also contains 80 to 250 parts by weight of powderedaluminum hydroxide on the basis of 100 parts by weight of said resincomponent of said polyethylene resin composition and a monoalkoxyorganic titanate compound.
 2. The polyethylene resin composition ofclaim 1, wherein said ethylene-vinyl acetate copolymer contains 10 to 75percent by weight of vinyl acetate.
 3. The polyethylene resincomposition of claim 1, wherein said resin component comprises 45 to 75parts by weight of polyethylene and 55 to 25 parts by weight of saidethylene-vinyl acetate copolymer.
 4. The polyethylene resin compositionof claim 1, wherein said monoalkoxy organic titanate compound is atleast one selected from the group consisting ofisopropyl-triisostearoyl-titanate andisopropyl-isostearoyl-dimethacryl-titanate.
 5. The polyethylene basecomposition of claim 1, which contains 100 to 200 parts by weight ofsaid aluminum hydroxide, the surface of said aluminum hydroxide beingtreated with a monoalkoxy organic titanate compound on the basis of 100parts by weight of said resin component.
 6. The polyethylene resincomposition of claim 1, which contains a fatty acid base compound havingthe following general formula: ##STR10## wherein R is an alkyl radicalhaving 4 to 22 carbon atoms,A is OH, NH₂, alkyloxy or alkenyloxy radicalhaving 1 to 22 carbon atoms, M is a metal atom belonging to Groups Ia,IIa, IIb, IIIa, IIIb, IVa and IVb of the Periodic Table, n is a positiveinteger corresponding to the valence of said metal M.